Displacement sensor

ABSTRACT

To be able to detect a displacement amount of a moving object by a resolution of from micrometer to nanometer by a simple structure.  
     An excitation coil  23  and a detection coil  25  are arranged to align and a magnetic body probe  27  in a conical shape a sectional area of which is change in a longitudinal direction is arranged in a state of being inserted into an air core portion of the excitation coil  23 . An output terminal from the detection coil  25  is connected to an amplifier  33  and a phase shifting circuit  35  is provided between the amplifier  33  and an input terminal of the excitation coil  23 . When the probe  27  of the magnetic body is moved at inside of the air core portion of the excitation coil  23,  inductance of the excitation coil  23  is changed, a phase difference is produced between an input signal inputted to the excitation coil  23  and an output signal outputted from the detection coil  25  and the phase shifting circuit  35  changes a frequency to nullify the phase difference. The displacement amount is detected from the frequency deviation at this occasion.

TECHNICAL FIELD

[0001] The present invention relates to a displacement sensor.

BACKGROUND ART

[0002] In order to control operation of a microactuator of a manipulatoror the like used in a micromachine or gene manipulation, it is requestedthat the microactuator is small-sized and light-weighed for detectingand measuring a displacement amount of a moving object by a resolutionof from micrometer to nanometer. Conventionally, in detecting andmeasuring a displacement amount by the resolution of from micrometer tonanometer, various systems have been proposed and reduced into practice.Representatively, there can be pointed out laser measurement by a methodof irradiating an object with laser light and detecting a phasedifference brought about in accordance with displacement of the object,a method of using a phenomenon of interference between the laser lightand reference light or the like.

[0003] A displacement amount in a nanometer order can be measured byusing laser measurement technology or the like. However, whereas a sizeof a microactuator is in an order of from several centimeters to ten andseveral centimeters, in the laser measurement, a light source, ameasuring portion for detecting and measuring a phase difference orinterference and the like become considerably large-sized. Further, theapparatus becomes expensive since a complicated optical system and ameasuring frequency at a high frequency are used and the like in orderto promote the resolution.

DISCLOSURE OF THE INVENTION

[0004] It is an object of the invention to resolve the problem of theconventional technology and to provide a displacement sensor fordetecting and measuring a displacement amount of a moving object by aresolution of from micrometer to nanometer by a simple structure andsuitable for small-sized and light-weighted formation.

[0005] In order to achieve the above-described above, a displacementsensor according to the invention is characterized in comprising anexcitation coil and a detection coil arranged in a predeterminedpositional relationship, an amplifier an input end of which is connectedto an output end of the detection coil, a phase shifting circuitprovided between an output end of the amplifier and an input end of theexcitation coil for shifting to nullify a phase difference by changing afrequency when the phase difference is produced between an inputwaveform inputted to the excitation coil and an output waveformoutputted from the detection coil, frequency measuring means fordetecting a frequency deviation produced by shifting the phase, and arod-like probe of a magnetic body which is inserted into at least one ofair core portions of the excitation coil and the detection coil and asectional area of which is changed in a longitudinal direction fordetecting a displacement amount of an object to be measured from thefrequency deviation produced by displacing the rod-like probe in thelongitudinal axis direction while maintaining a resonating state of aclosed loop including a space between the excitation coil and thedetection coil.

[0006] Further, the displacement sensor according to the invention ischaracterized in that the excitation coil is constituted by connectingtwo coils wound such that polarities thereof are directed reverse toeach other in series.

[0007] Further, a displacement sensor according to the invention ischaracterized in comprising a light emitting element for making lightincident on an object to be measured, a light receiving element fordetecting a reflected wave from the object to be measured, an amplifieran input end of which is connected to an output end of the lightreceiving element, a phase shifting circuit provided between an outputend of the amplifier and an input end of the light emitting element forshifting to nullify a phase difference by changing a frequency when thephase difference is produced between an input waveform inputted to thelight emitting element and an output waveform outputted from the lightreceiving element, and frequency measuring means for detecting afrequency deviation produced by shifting the phase for detecting adisplacement of the object to be measured from the frequency deviationproduced by displacing the object to be measured while maintaining aresonance of a closed loop including a space between the light emittingelement and the light receiving element.

[0008] The displacement sensor according to the invention is constructedby a constitution in which a detection coil, an amplifier, a phaseshifting circuit and an excitation coil are connected in this order anda rod-like probe of a magnetic body a sectional area of which is changedin a longitudinal axis direction is arranged to be inserted into atleast one of air core portions of the detection coil and the excitationcoil. According to the constitution, when the rod-like probe isdisplaced in the longitudinal axis direction, a frequency deviation isproduced in accordance with a displacement amount while maintaining aresonating state of a closed loop including a space between theexcitation coil and the detection coil and therefore, the displacementamount of the rod-like probe can be detected. Since a frequencydeviation of several kHz is produced by a displacement amount of 1 mm,there can be realized a displacement sensor capable of detecting thedisplacement amount by a resolution of 0.1 through 0.01 micrometer,detecting and measuring a displacement amount of a moving object by aresolution in a micrometer to nanometer order by a simple structure andsuitable for small-sized and light-weighted formation.

[0009] Further, the excitation coil is constituted by connecting twocoils wound such that polarities thereof are directed reverse to eachother in series. In this case, magnetic fields thereof are canceled byeach other at a vicinity of a point of connecting the two coils and whenthe two coils are provided with the same characteristic, a substantiallynullified magnetic field is constituted to balance. By constructing aconstitution of arranging a probe of a magnetic body to be inserted intoan air core portion thereof, a sensitivity with respect to thedisplacement is increased, a frequency deviation equal to or larger than10 kHz is produced by a displacement amount of 1 mm and therefore, therecan be realized a displacement sensor for detecting and measuring thedisplacement amount of the moving object by a resolution at a micrometerlevel by a simple structure and suitable for small-sized andlight-weighted formation.

[0010] Further, a displacement sensor according to the invention isconstructed by a constitution in which a light emitting element and alight receiving element are used, light is made to be incident on anobject to be measured, a reflected wave therefrom is detected and thelight receiving element, an amplifier, a phase shifting circuit and thelight emitting element are connected in this order. According to theconstitution, when the object to be measured is displaced, a frequencydeviation is produced in accordance with the displacement amount whilemaintaining a resonating state of a closed loop including a spacebetween the light emitting element and the light receiving element andtherefore, the displacement amount of the object to be measured can bedetected. Since a frequency deviation equal to or larger than 10kHz isproduced by a displacement amount of 1 mm, there can be realized adisplacement sensor for detecting and measuring the displacement amountof the moving object by a resolution in a micrometer through nanometerorder by a simple structure and suitable for small-sized andlight-weighted formation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a view showing a constitution of a-displacement sensorof an inductance directly measuring type according to a first embodimentof the invention.

[0012]FIG. 2 is a diagram designating the abscissa by a displacementamount of a probe and designating the ordinate by inductance of a coiland showing a relationship therebetween according to the firstembodiment of the invention.

[0013]FIG. 3 is a block diagram of a displacement sensor of aninductance type according to a second embodiment of the invention.

[0014]FIG. 4 is a block diagram of a displacement sensor of aninductance type having a higher sensitivity according to a thirdembodiment of the invention.

[0015]FIG. 5 is a block diagram of a displacement sensor of an opticaltype according to a fourth embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0016] A detailed explanation will be given of embodiments of theinvention in reference to the drawings as follows. FIG. 1 is a viewshowing a constitution of a displacement sensor 1 of an inductancedirectly measuring type according to a first embodiment. Thedisplacement sensor 1 is constituted by a coil 3, a probe 5 of amagnetic body in a conical shape a sectional area of which is changed ina longitudinal axis direction, an inductance meter 7 arranged betweentwo terminals of the coil 3 and a displacement conversion portion 9 forconverting a detected value of the inductance meter 7 into adisplacement amount. The probe 5 of the magnetic body is arranged to beinserted into an air core portion of the coil 3.

[0017] According to the constitution, when the probe 5 of the magneticbody is displaced at inside of the air core portion of the coil 3 in alongitudinal axis direction (x), inductance of the coil 3 is changed.That is, it is generally known that inductance of a coil having apermeability μ of an air core portion, a sectional area A, a length L ina longitudinal direction and a turn number N is proportional toμ*A*N*N/L. Hence, when the probe 5 of the magnetic body the sectionalarea of which is changed in the longitudinal direction is displaced inthe longitudinal direction (x) at inside of the air core portion of thecoil 3, in accordance with a displacement amount thereof, a volume ofthe probe disposed in the air core portion of the coil 3 is changed, μis substantially changed and the inductance is changed.

[0018]FIG. 2 is a diagram designating the abscissa by the displacementamount of the probe 5 and designating the ordinate by the inductance ofthe coil 3 and showing a relationship therebetween. Now, it is assumedthat a direction of increasing the displacement amount is a direction ofincreasing the volume of the probe 5 of the magnetic body disposed atthe air core portion of the coil 3. In this case, with an increase inthe displacement amount, μ is substantially increased and the inductanceof the coil 3 is also increased. When a rate of changing the sectionalarea of the probe 5 in the longitudinal direction is pertinentlydesigned, a change in the displacement amount and a change in theinductance can be made to be linear.

[0019] In this way, the displacement amount of the probe 5 can beprovided by a simple structure by displacing the probe 5 of the magneticbody the sectional area of which is changed in the longitudinaldirection at inside of the area core portion, detecting the change inthe inductance of the coil 3 at that occasion by the inductance meter 7and converting a detected value thereof into the displacement amount bythe displacement amount conversion portion.

[0020]FIG. 3 is a block diagram of a displacement sensor 21 of aninductance type according to a second embodiment. An excitation coil 23and a detection coil 25 are arranged by aligning longitudinal axes ofrespective air core portions thereof commonly. Further, a probe 27 in aconical shape a sectional area of which is changed in a longitudinaldirection is provided and the probe 27 is constituted by a magneticbody. Further, the probe 27 is arranged in a state of being insertedinto the air core portion of the excitation coil 23. An output terminalfrom the detection coil 25 and an input terminal to the excitation coil23 are connected to a signal processing portion 31. In the signalprocessing portion 31, the output terminal from the detection coil 25 isconnected to an amplifier 33 and a phase shifting circuit 35 is providedbetween the amplifier 33 and the input terminal of the excitation coil23. A frequency deviation detector 37 is connected to the phase shiftingcircuit 35, further, a displacement amount calculator 39 is connected tothe frequency deviation detector 37.

[0021] In this way, by forming a single closed loop resonating circuitby including a space between the excitation coil 23 and the detectioncoil 25, that is, a magnetic circuit of the air core portion includingthe excitation coil 23—the probe 27—the detection coil 25, supplyingenergy from a power source, not illustrated, and pertinently setting afrequency-gain phase characteristic of the phase shifting circuit 35,resonance can be continued. An inner constitution of the phase shiftingcircuit 35 and operation thereof in such a closed loop resonatingcircuit is described in details in JP-A-9-145691.

[0022] In FIG. 3, when the probe 27 of the magnetic body is displacedand moved in the air core portion of the excitation coil 23, since theprobe 27 of the magnetic body is formed in the conical shape, the volumeof the magnetic body in the air core portion is changed. Thereby, as hasbeen explained in reference to FIG. 2, the inductance of the excitationcoil 23 is changed and there is brought about a change in the magneticcircuit of the space between the excitation coil 23 and the detectioncoil 25, that is, the magnetic circuit of the air core portion includingthe excitation coil 23—the probe 27—the detection coil 25. In accordancetherewith, a phase difference is produced between an input signalinputted to the excitation coil 23 and an output signal outputted fromthe detection coil 25 and the phase shifting circuit 35 changes afrequency to nullify the phase difference. A frequency deviation at theoccasion is detected by the frequency deviation detector 37 and thedisplacement amount is outputted by the displacement calculator 39 forprocessing a relationship between the frequency deviation and thedisplacement amount.

[0023] A frequency deviation equal to or larger than several 10 kHz isproduced by a displacement amount of 1 mm and therefore, thedisplacement amount can be detected by a resolution at a micrometerlevel. Since the frequency deviation is in an order of several 10 kHz, aprocessing frequency of the signal processing portion is comparativelylow and the signal processing portion can be constructed by a simplecircuit constitution.

[0024]FIG. 4 shows a displacement sensor 22 of an inductance type havinga higher sensitivity according to a third embodiment. The same notationsare attached to constituent elements common to those of FIG. 3 and anexplanation thereof will be omitted. In this case, there are used coils24 a and 24 b wound such that pluralities thereof are directed reverseto each other and connected in series for an excitation coil 24.According to the constitution, magnetic fields are canceled by eachother at a vicinity of a point of connecting the two coils 24 a and 24 band when the two coils 24 a and 24 b are provided with the samecharacteristic, a substantially nullified magnetic field is constitutedto balance. By constructing a constitution of arranging the probe 27 ofthe magnetic body to insert into the air core portion, a change in thebalance by inserting the probe 27 of the magnetic body can be detectedby a detection coil 26 and a sensitivity with respect to a displacementis further increased.

[0025] Since a frequency deviation equal to or larger than 10 kHz isproduced by a displacement amount of 1 mm, there can be realized adisplacement sensor for detecting and measuring a displacement amount ofa moving object by a resolution at a micrometer level and suitable forsmall-sized and light-welded formation by a simple structure.

[0026] A positional relationship between the excitation coil and thedetection coil may be established by an arranging method by which aconstant positional relationship is fixed by arranging the excitationcoil and the detection coil to align longitudinal axes of respective aircore portions thereof commonly as in FIG. 3, arranging the detectioncoil concentrically at an outer periphery of the excitation coil as inFIG. 4 or the like. The probe may be arranged by being inserted into atleast one of the air core portions of the excitation coil and thedetection coil. Other than a conical shape, other shape by which asectional area thereof is changed such as a portion of a cone, afunction body of rotation constituting an axis of rotation by alongitudinal axis thereof, a portion of a pyramid or the like can beused for the probe.

[0027] In this way, there can be realized a displacement sensor fordetecting and measuring a displacement amount of a moving object by aresolution of from micrometer to nanometer and suitable for small-sizedand light-weighted formation by simple constitutions of the excitationcoil, the detection coil and the probe and the signal processingportions having a comparatively low processing frequency.

[0028]FIG. 5 is a block diagram of a displacement sensor 51 of anoptical type according to a fourth embodiment. A light emitting element53 and a light receiving element 55 are provided to be opposed to anobject 57 to be measured. An output terminal from the light receivingelement 55 and an input terminal to the light emitting element 53 areconnected to the signal processing portion 31. Constitution andoperation of the signal processing portion 31 are similar to those ofFIG. 2 and therefore, an explanation thereof will be omitted. In thisway, a single closed loop resonating circuit is formed by including aspace between the light emitting element 53 and the light receivingelement 55, that is, a path of light of the light emitting element53—the object 57 to be measured—the light receiving element 55.

[0029] In FIG. 5, when the object 57 to be measured is displaced and achange is brought about at the space between the light emitting element53 and the light receiving element 55, that is, in a length of the pathof the light of the light emitting element 53—the object 57 to bemeasured—the light receiving element 55, in accordance therewith, aphase difference is produced between an input signal inputted to thelight emitting element 53 and an output signal outputted from the lightreceiving element 55 and the phase shifting circuit 35 changes thefrequency to nullify the phase difference. The frequency deviation atthis occasion is detected by the frequency deviation detector 37 and thedisplacement amount is outputted by the displacement amount calculator39 for processing a relationship between the frequency deviation and thedisplacement amount.

[0030] Since a frequency deviation equal to or larger than 100 kHzthrough 1000 kHz is produced by a displacement amount of 1 mm, thedisplacement amount can be detected by a resolution in a nanometerorder. Since the frequency deviation is utilized, a processing frequencyof the signal processing portion can be produced by a comparativelysimple circuit constitution.

[0031] In this way, there can be realized a displacement sensor fordetecting and measuring a displacement amount of a moving object by aresolution of from micrometer to nanometer and suitable for small-sizedand light-weighted formation by simple constitutions of the lightemitting element, the light receiving element and the signal processingportion having a comparatively low processing frequency.

Industrial Applicability

[0032] The displacement sensor according to the invention can detect andmeasure the displacement amount of the moving object by the resolutionof from micrometer to nanometer by a simple structure and is suitablefor small-sized and light-weighted formation.

1. A displacement sensor characterized in comprising an excitation coiland a detection coil arranged in a predetermined positionalrelationship, an amplifier an input end of which is connected to anoutput end of the detection coil, a phase shifting circuit providedbetween an output end of the amplifier and an input end of theexcitation coil for shifting to nullify a phase difference by changing afrequency when the phase difference is produced between an inputwaveform inputted to the excitation coil and an output waveformoutputted from the detection coil, frequency measuring means fordetecting a frequency deviation produced by shifting the phase, and arod-like probe of a magnetic body which is inserted into at least one ofair core portions of the excitation coil and the detection coil and asectional area of which is changed in a longitudinal direction fordetecting a displacement amount of an object to be measured from thefrequency deviation produced by displacing the rod-like probe in thelongitudinal axis direction while maintaining a resonating state of aclosed loop including a space between the excitation coil and thedetection coil.
 2. The displacement sensor according to claim 1,characterized in that the excitation coil is constituted by connectingtwo coils wound such that polarities thereof are directed reverse toeach other in series.
 3. A displacement sensor characterized incomprising a light emitting element for making light incident on anobject to be measured, a light receiving element for detecting areflected wave from the object to be measured, an amplifier an input endof which is connected to an output end of the light receiving element, aphase shifting circuit provided between an output end of the amplifierand an input end of the light emitting element for shifting to nullify aphase difference by changing a frequency when the phase difference isproduced between an input waveform inputted to the light emittingelement and an output waveform outputted from the light receivingelement, and frequency measuring means for detecting a frequencydeviation produced by shifting the phase for detecting a displacement ofthe object to be measured from the frequency deviation produced bydisplacing the object to be measured while maintaining a resonance of aclosed loop including a space between the light emitting element and thelight receiving element.